Maybe Percy is chosen by the Fates to be their champion in a battle against an ancient evil that threatens to disrupt the very fabric of fate. He has to team up with some unlikely allies, like minor gods who are also concerned about the balance of fate. He would have to learn new skills and face challenges that test his limits.
Another plot could be that the Fates are in trouble themselves. Some dark force has managed to infiltrate their realm and is starting to manipulate the threads of fate. Percy, being the hero he is, steps in to save them. Along the way, he learns more about the inner workings of fate and how every decision, no matter how small, can have a huge impact on the world.
Well, a plot idea could involve Percy being cursed by the fates to forget his own identity. He then has to go on a journey to rediscover who he is while still fulfilling his duties as the champion of the fates. Along the way, he might meet old friends who don't recognize him at first, and he has to prove himself to them. Or perhaps the fates send Percy on a mission to prevent a prophecy from coming true that would destroy the entire demigod world. This would involve him traveling to different mythological places and facing powerful enemies.
Well, a plot could involve Percy being sent on a special mission by the Fates. Since they control destiny, this mission might be crucial for the balance of the entire demigod world. He could have to face enemies that are normally out of reach for regular demigods. Along the way, he discovers secrets about his adoption that change his perspective on his life and his role among his peers.
Well, perhaps a plot where Percy discovers that being married to the Fates gives him the ability to see snippets of the future, but it's all jumbled up. He then has to work with the Fates to figure out how to use this new power properly. Also, there could be a story line where other gods are jealous of Percy's connection to the Fates through marriage and try to undermine him.
One idea could be Percy going on a quest that was pre - ordained by the Fates. He discovers that his every move is part of a larger plan they have for the demigod world. For example, he might be sent to retrieve an ancient artifact that holds the key to maintaining the balance between the gods and the Titans, and along the way, he has to face challenges that test his loyalty to the Fates' plan.
Well, perhaps in the fanfiction, the Angel of God is a messenger to Percy, warning him of a great catastrophe that will befall the demigod world. Percy then has to gather all the demigods and prepare them for this threat. The angel could also have the power to bestow temporary divine abilities on Percy and his friends, which they use to battle an army of dark creatures. Or it could be that the angel is actually a lost soul from a previous era, and Percy has to solve the mystery of its past to get its help in saving his world.
One idea could be that the Evil God manipulates Percy's friends against him. For example, making Annabeth doubt Percy's loyalty through false visions. Another could be that the Evil God corrupts the demigod world's magic, turning it against the heroes. Maybe the water Percy usually controls starts to harm him instead of help.
One idea could be Percy having to face a new and powerful monster that is a combination of multiple mythological creatures. This would test his skills and force him to come up with new battle strategies.
Well, a plot could revolve around Percy accidentally getting this 'God of Sex' title and trying to figure out how to get rid of it. He might go on a quest to find a way to reverse it. Along the way, he meets other characters who either want to use his power for their own gain or help him out of the mess. It could also involve some comical situations where his friends misunderstand his new powers and get into all sorts of awkward situations.
One idea could be Percy having to protect a group of special children who have unique powers related to the Greek gods. Maybe they are descendants of minor gods and are being hunted by some ancient monsters. Another plot could involve Percy teaching these children about their heritage and how to control their powers in a world that doesn't fully understand them.
Perhaps Percy as the God of Justice has to judge the actions of the Olympian gods themselves. This would create a lot of tension as he tries to hold them accountable for their past misdeeds. Or he could be in charge of a special court for demigods who have committed crimes but have valid reasons for their actions, and he has to balance justice and mercy.